1. Field of the Invention
The present invention relates to a printed wiring board for use in mounting or packaging electronic parts therein, and in particular a printed wiring board having a cavity for mounting electronic parts therein and a method for manufacturing thereof, thereby enabling to mount the electronic parts, for example on a mother board, etc., with high density thereof.
2. Description of the Prior Art
Conventionally, mounting or packaging is carried out by loading plural numbers of electronic parts or components, such as semiconductor elements and/or chip-like parts, etc., on a surface of a plate-like printed wiring board, on which a predetermined circuit patterns are formed, so as to form a module (or a module board), and this module obtained is further piled on a motherboard, etc., flatly, in a form of a hybrid IC.
By referring to FIG. 11, explanation will be given on packaging condition where the electronic parts are mounted on the plate-like printed wiring board 10 of the conventional art, so as to form the module therewith, and after that this is piled on the motherboard flatly.
First of all, on the plate-like printed wiring board 10 of a single or multi-layered substrate or board are formed conductor layers 3, such as predetermined circuit patterns, lands for use in connection of electronic parts, plated through-holes 4, and side end-surface electrodes 5, etc. After that, chip-like electronic parts 3 are fixed upon the surfaces of the lands 3, which are formed on the surface of the plate-like printed wiring board 10 mentioned above, thereby being electrically connected therewith.
Next, the module board mounting the plural numbers of the chip-like electronic parts 30 thereon is heated and mounted, to be connected onto connector terminals 45 provided on the motherboard 40, with using side end-surface electrodes 5 which are provided on the plate-like printed wiring board 10. However, for the purpose of mounting the module board, on which the plural number of the chip-like electronic parts 30 are mounted, on the motherboard 40 with stability, in general, no such an element, as the chip-type electronic parts 30, is mounted on a lower surface of said the plate-like printed wiring board 10, which defines a reverse surface side thereof.
On the other hand, when the module board, being formed by mounting the chip-like electronic parts 30 on both side surfaces of the plate-like printed wiring board 10 mentioned above, is mounted on the motherboard 40, it is fixed on the motherboard 40 through a spacer plate, a connector, and/or a pin board, etc., which is/are attached on the reverse side flat surface of the module plate, i.e., a mounted side (a lower side) thereof.
Accompanying by high- and multi-functions required for electronic and electric equipments in the recent years, those requirements of such the high- and multi-functions are also demanded onto the module board and the hybrid IC, etc. Accordingly, also for the printed wiring board, such the requirements of such the high- and multi-functions, as well as of high density and minuteness in lines to be formed, are made strongly, therefore the printed wiring board is needed to be more complex in the form and structure thereof.
For achieving such the high-density mounting required for the printed wiring board, so-called a flat through-hole is already known, as is disclosed in Japanese Patent Laying-open No. Hei 4-91489 (1992), wherein electrically insulating resin is filled up and harden within the plated through-holes formed on the wiring board, to be formed with connector portions, such as the bonding pads and/or the connector lands, upon the surfaces thereof, thereby utilizing even the surfaces of the plated through-holes formed thereon.
As was mentioned in the above, in the conventional art, in general, no such the chip-like electronic element is allowed to be mounted on the reverse side surface (i.e., the lower side surface) of the plate-like printed wiring board, because of the surface to be mounted on. However, for the purpose of improving the mounting density, it is required that the chip-like electronic parts can be mounted, not only the surface of the plate-like printed wiring board, but also on the reverse side surface thereof. And, for mounting such the module board, on both surfaces of which the chip-like electronic parts are mounted, on the motherboard closely contact therewith, there is a necessity of floating it up from the surface of the motherboard, with aid of attaching the spacers and/or the connectors at a lower side (i.e., the lower surface) of the module plate, which faces or confronts to the motherboard.
However, if floating up the plate-like printed wiring board by means of such the spacers and/or the connecters, so as to mount it on the motherboard, it is difficult to mount it on the motherboard with stability, i.e., it is difficult to mount the chip-like electronic parts on the lower side (i.e., the lower surface) of the plate-like printed wiring substrate, flatly and closely contacted with, as well as, with high mounting density thereof.
An object of the present invention, accordingly, for dissolving such the problems of the conventional art mentioned above, is to provide a printed wiring board having a cavity for mounting the electronic parts therein and a method for manufacturing thereof, namely, enabling to mount the chip-like electronic parts, not only the surface of the plate-like wiring board, but also on the reverse side surface thereof, thereby achieving mounting or packaging of the chip-like electronic parts with high density, while keeping them closely contact with, and horizontally on the motherboard.
According to the present invention, for accomplishing such the object as mentioned above, there is provided a printed wiring board, comprising:
an upper wiring substrate having flat surfaces on both sides thereof;
a lower plate body being fixed on the reverse side surface said upper wiring substrate, and being formed with a cavity therein, for receiving an electronic part within an inside thereof;
conductor layers being formed upon the surface of said upper wiring substrate, for mounting an electronic part thereon;
conductor layers being formed on a reverse side surface said upper wiring substrate, for mounting an electronic part thereon, facing to a region where said cavity is defined by said lower plate body, and being electrically connected with the conductor layers formed on the surface of said upper wiring substrate, respectively; and
external electrodes being formed on portions of an outer peripheral surface of said upper wiring substrate and said lower plate body formed in one body, and being electrically connected with said conductor layers, respectively, for mounting said printed wiring board on an outside substrate.
Also, according to the present invention, on the printed wiring board mentioned above, a plated through-hole is formed between the surfaces of the upper wiring substrate, for interconnecting the conductor layers, to be mounted with an electronic parts on the both sides of said upper wiring plate, and is filled with electrically non-conductive resin in an inside thereof, or alternatively a flat through-hole may be formed in the place thereof. Herein, the xe2x80x9cflat through-hole (or flat plated through-hole)xe2x80x9d means the structure or method for forming the conductor layer(s) to be a circuit conductor or a conductor pad for use in mounting of electronic parts thereon, with aggressively utilizing both side surfaces or one surface of so-called xe2x80x9ca buried through-holexe2x80x9d formed in the substrate, within plated electrode of which is filled up or buried the non-conductive resin, and it is also the same in the explanations given hereinafter. Also, in the following explanations, the xe2x80x9cthrough-holexe2x80x9d means the plated through-hole, having the inner electrode formed on the wall surface of the hole through plating, even when omitting the word xe2x80x9cplatedxe2x80x9d at a head thereof.
Further, according to the present invention, in the printed wiring board mentioned above, said external electrodes are formed on side-end surfaces of said printed wiring board, or alternatively on a lower end surface of said printed wiring board. And, said external electrodes can be made of metal conductors of a xe2x80x9cbottomed through-holexe2x80x9d, each being formed on said printed wiring board penetrating through the upper wiring substrate and the lower plate body and is closed at a lower end thereof.
Further, according to the present invention, in the printed wiring board mentioned above, said lower plate body is formed in either a gate-like shape or a frame-like shape in a plane view thereof, and said lower plate body has a thickness being a little bit larger than that of the electronic part received within said cavity formed. In particular, depth (h) of the cavity of said lower plate body lies within a range from 30% to 90% of thickness (t) of said printed wiring board. Moreover, it is preferable that openings or gaps are hermetically sealed with a resin or molding material, after the electronic part is mounted to be received within the cavity of said lower plate body.
Also, according to the present invention, for accomplishing the object mentioned above, there is further provided a method for manufacturing a printed wiring board, comprising a sequence of the following steps:
(a) forming a through-hole on an upper wiring substrate, on both surfaces of which are lamented conductor foils, and filling up filler within said through-hole formed;
(b) forming predetermined conductor layers for connection of electronic parts thereon on one surface of said upper wiring substrate, which are electrically connected through said through-hole formed;
(c) preparing a lower plate boy, being laminated with conductor foil on at least one surface thereof and formed with a cavity for receiving an electronic part in a part thereof, and bonding said lower plate body onto the one surface of said upper wiring substrate with a surface opposing to that being laminated with the conductor foil; and
(d) forming external electrodes for mounting said printed wiring board on an outside substrate, on portions of an outer peripheral surface of said upper substrate and said lower plate body formed in one body, with predetermined conductor layers for connecting electronic parts thereon.
According to the present invention, in the method for manufacturing a printed wiring board mentioned above, the through-hole formed in the step of the (a) mentioned above is a flat through-hole, in which conductor layers are formed on both end surfaces of the filler filled up within said through-hole, or said cavity is filled up with resin in advance when forming the predetermined conductor layers for connecting the electronic parts thereon in said step(d), or the step for forming said external electrodes in said step (d) includes a step for forming bottomed through-holes, each of which penetrates through said upper substrate and said lower plate body bonded to each other and is closed at a lower end thereof.